1. Field of the Invention
The present invention relates to an extraction process for recovering intermediates and product from a process residue and more particularly, to a process for the recovery of adiponitrile and its precursors from a process residue obtained from the preparation of adiponitrile by the hydrocyanation of butadiene.
2. Description of the Prior Art
A general disclosure of typical processes to which the present invention may be applied is found in the publication entitled "Hexamethylene Diamine" in The Process Economics Program Report No. 31-A, Stanford Research Institute, Menlo Park, C.A.; September, 1972. More particularly, the hydrocyanation process to which the present invention can be applied is disclosed in U.S. Pat. Nos. 3,496,215 issued on Feb. 10, 1970 3,496,218 issued on Feb. 17, 1970 3,542,847 issued on Nov. 24, 1970 and 3,752,839 issued on Aug. 14, 1973. The residue from the above-disclosed process is obtained by removing the substantial portion of desired products, unreacted materials and intermediates from the reactor effluent, separating solvent and other volatiles from the resultant stream for recycle to the reactor and thereafter obtaining a concentrated waste system as residue. The process of the present invention recovers valuable products from such residue.
Solvent extraction for recovery of organics has been considered extensively, e.g., Separation Processes, King, C.J., Chem. Eng. Series, McGraw Hill, 1971, but has not been applied to the type of waste stream herein disclosed using the claimed solvents. Common solvents are foreign to the hydrocyanation system and must be rigorously separated from the extract before the extract can be returned to the system. Such a procedure is unsatisfactory in the commercial operation to which the present invention is applied.